On the Distillation of recent and of dried Ft get aides. 167 

 ing those of Reaumur, the centigrades, &c, as being too 

 few, and decimal divisions unnecessary in a thermomctri- 

 cal scale. 



Hence it will follow, that being placed at 62° of Fah- 

 renheit, 150° will be the boiling, and minus SO , the freez- 

 ing points of water ; and all other points on Fahrenheit's 

 scale may be reduced to this, by subtracting 62 for any 

 degree above of Fahrenheit ; and adding 62 for any degree' 

 lelow 0. . - 



I shall only add, at present, that there is a very convenient 

 mechanical mode of adjusting this scale in the construction 

 of thermometers. ■. ' 



For ordinary meteorological purposes, a scale of this kind 

 extending to 65 degrees above 0, and as many degrees below 

 v), will be sufficient. 



Rd. Walker. 



Queen-Street, Oxford, 

 Feb. 17, 1309. 



XXVII. On the Difference between the Products obtained 

 by Distillation of recent and of dried Vegetables t By 

 Mr. Gab den, of Old Compion Street, London *. 



X hat most recent vegetable bodies during the process of 

 desiccation undergo a material change in their external ap- 

 pearances becomes evident from mere inspection ; but that 

 an alteration frequently takes place in their physical proper- 

 ties, and also among their constituent principles, by that 

 process, has not-, perhaps, in every case, been so clearly 

 established. 



Our knowledge indeed of the physical properties of vege- 

 table substances, obtained from an acquaintance with their 

 chemical composition, has hitherto made but little progress; 

 arising, no doubt, from the exceeding alterability of their 

 nature, when subjected to those processes usually employed 

 for disuniting their component parts ; some of their ingre- 

 dients being too volatile to be retained, while others become 

 so modified by the action of moderate temperature*, as to 



* Communicated by Mr, Garden, 



L<* / render 



